1. Field of Invention
The present invention relates to a cathode-ray tube apparatus such as a color-picture tube apparatus and, more particularly, to a cathode-ray tube apparatus wherein electron beams emitted from a plurality of electron guns are deflected by a plurality of deflection devices and the phosphor screen has a plurality of regions which are dividedly scanned.
2. Description of Related Art
Recently, a high resolution cathode-ray tube has been more and more demanded for high-definition TV broadcasting and large screen display accompanied therewith. Particularly, to display such high definition pictures, a much higher performance has been demanded in the display screen. To achieve these demands, flatness of the screen, high resolution of pictures and reduction of aberration in deflection are absolutely necessary. At the same time, the weight and thickness of the cathode-ray tube must be reduced.
In the prior art, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-36363 has disclosed a cathode-ray tube apparatus which satisfies such demands. According to this proposal, an integrated phosphor screen without discontinuity is formed on an inner surface of a flat, rectangular face plate. An electron gun is disposed within a neck of each of a plurality of funnels provided on a rear plate opposing the face plate. Electron beams emitted from such a plurality of the electron guns are deflected by a plurality of deflection devices disposed corresponding to the respective electron guns. The phosphor screen has a plurality of regions which are dividedly scanned by the electron guns. Then divided images obtained by such divisional scanning are joined together to produce a synthesized image and the synthesized image is displayed on the phosphor screen.
In the cathode-ray tube apparatus, the plurality of the deflection devices disposed corresponding to the respective electron guns are driven by a plurality of independent deflection driving circuits like an ordinary cathode-ray tube apparatus in which a single phosphor screen is entirely scanned with electron beams emitted from a single electron gun so as to produce a single image on the phosphor screen.
Further in such a cathode-ray tube apparatus, divided images displayed in adjacent regions must be smoothly continuous with each other visually without any sense of incongruity across borders between the regions scanned independently of one another. For this purpose, in the cathode-ray tube apparatus, a plurality of the deflection devices disposed corresponding to the plurality of the electron guns are adjusted in position so that they are located at optimum positions. Further, the deflection driving circuits corresponding to the respective deflection devices are adjusted into optimum condition. Through these adjustments, it is intended so that the division pictures displayed in respective regions are smoothly continuous with each other visually without sense of incongruity between the division pictures displayed in the adjacent regions.
U.S. Pat. No. 5,498,921 discloses a method for adjusting the position of deflection devices. According to this method, preliminarily, a plurality of deflection devices are fixed at reference positions on a reference fixing board and the relative positions thereof are adjusted to a predetermined position. After that, the deflection devices are mounted to funnels in a cathode-ray tube together with the reference fixing board. Then, the position of the reference fixing board is adjusted relative to the funnels. Accordingly, the mounting positions of the plurality of the deflection devices are adjusted at the same time.
Further, Jpn. Pat. Appln. KOKAI Publication No. 8-241,684 discloses a method for making orbits of electron beams emitted from a plurality of electron guns coincide with reference axes in respective regions to be scanned independently of one another.
However, a plurality of the deflection driving circuits disposed corresponding to the plurality of the deflection devices must be adjusted individually because the scanning range with electron beam differs depending on the deflection device and the linearity of each region differs from the central portion to the peripheral portion thereof. Further, discontinuity between adjacent regions must be eliminated so as to produce a continuous image without discontinuity.
As a result, in the cathode-ray tube apparatus having such a construction, if the number of the regions of the phosphor screen increases, the number of the deflection driving circuits also increases, so that time needed for adjustment of those components increases. To obtain a synthesized image visually without any sense of congruity by synthesizing divided images displayed in the respective regions, such adjustments are necessary, first, that the linearity in the central portion and peripheral portion of each divided image is smoothly continuous other visually without sense of incongruity, and second, so that the divided images are continuous with each other at the boundaries between adjacent regions.
However, in the adjustment of the deflection driving circuit, first, one of those adjustments, for example, adjustment of linearity in respective regions is carried out and then adjustment for ensuring continuity between adjacent regions is carried out. In this case, when the latter adjustment is performed, the initially adjusted linearity is deviated. Thus, these two kinds of adjustments must be performed repeatedly. Additionally, these adjustments are very difficult to do and take long time.